A child theme is a theme that inherits the functionality of another theme, called the parent theme (The7 here). Child themes allow you to modify, or add to the functionality of that parent theme. A child theme is the best, safest, and easiest way to modify an existing theme, whether you want to make a few tiny or extensive changes. By keeping your customization in a child theme you can always keep the parent theme up-to-date without losing your modification.
Basic example of a child theme is provided within full theme package: The7_v.x.x.x.zip/Child Theme Example/dt-the7-child.zip
Unzip it into …/wp-content/themes/ folder. There is nothing specific about child theme functioning – it works the same as a standard WP child theme. You can find more information here:
Besides the default templates (header.php, footer.php, page templates, etc.), if you want to modify any core functions from ../THEME-NAME/inc/helpers.php, template-hooks.php, etc, copy the entire function which you want to modify to your child theme’s functions.php and edit it there.
Copy Parent theme setting to Child
When activating a child theme, settings are reverted to default. So if you decide to use a child theme later (after configuring a parent theme), please use Theme options > Import & export to transfer settings.